Decadal losses of canopy‐forming algae along the warm temperate coastline of Brazil

The loss of canopy‐forming seaweeds from urbanized coasts has intensified in response to warming seas and non‐climatic pressures such as population growth and declining water quality. Surprisingly, there has been little information on the extent of historical losses in the South‐western Atlantic, which limits our ability to place this large marine ecosystem in a global context. Here, we use meta‐analysis to examine long‐term (1969–2017) changes to the cover and biomass of Sargassum spp. and structurally simple algal turfs along more than 1,000 kilometres of Brazil's warm temperate coastline. Analysis revealed major declines in canopy cover that were independent of season (i.e., displaying similar trends for both summer and winter) but varied with coastal environmental setting, whereby sheltered bays experienced greater losses than coastal locations. On average, covers of Sargassum spp. declined by 2.6% per year, to show overall losses of 52% since records began (ranging from 20% to 89%). This contrasted with increases in the cover of filamentous turfs (24% over the last 27 years) which are known to proliferate along human‐impacted coasts. To test the relative influence of climatic versus non‐climatic factors as drivers of this apparent canopy‐to‐turf shift, we examined how well regional warming trends (decadal changes to sea surface temperature) and local proxies of coastal urbanization (population density, thermal pollution, turbidity and nutrient inputs) were able to predict the changes in seaweed communities. Our results revealed that the most pronounced canopy losses over the past 50 years were at sites exhibiting the greatest degree of coastal warming, the highest population growth and those located in semi‐enclosed sheltered bays. These findings contribute knowledge on the drivers of canopy loss in the South‐western Atlantic and join with global efforts to understand and mitigate declines of marine keystone species.     

Relative contribution of environmental and nutritional variables to net primary production of Cynodon dactylon (Linn.) Pers in the riparian zone of a Three Gorges tributary

Our knowledge of fundamental drivers of terrestrial net primary production (NPP) is crucial for improving the predictability of ecosystem stability under global climate change. However, the patterns and determinants of NPP are not fully understood, especially in the riparian zone ecosystem disturbed by periodic drought–rewetting (DRW) cycles. The environmental (flooding time, pH, moisture, and clay content) and nutritional properties (soil organic carbon, total nitrogen, total phosphorus, ammonium (NH₄⁺‐N), nitrate (NO₃^‐‐N), and C:N:P stoichiometry) were investigated in the riparian zone of Pengxi River‐a typical tributary of Three Gorges Reservoir (TGR). Structure equation modeling was performed to evaluate the relative importance of environmental and nutritional properties on NPP of Cynodon dactylon (Linn.) Pers (C. dactylon)‐a dominating plant in the riparian zone of TGR. Our results indicated that NPP was much lower under much severe flooding stress. All of these variables could predict 46% of the NPP variance. Nutrient use efficiency (NUE) was one of the most critical predictor shaping the change of NPP. Specifically, flooding stress as a major driver had a direct positive effect on soil moisture and soil clay content. The soil clay content positively affects the soil C: N ratio, which further had an indirect negative impact on NPP by mediating NUE. Overall, our study provided a comprehensive analysis of the effects of the combined effect of environmental and nutrient factors on NPP and showed that continuous DRW cycles induced by hydrological regime stimulate the decrease of NPP of C. dactylon by changing NUE strategies. Further research is needed to explore the responses of NPP and NUE under different land use to DRW cycles and to investigate the DRW effects on the combined effect of environmental and nutrient factors by in situ experiments and long‐term studies.     

Exploring the functional meaning of head shape disparity in aquatic snakes

Phenotypic diversity, or disparity, can be explained by simple genetic drift or, if functional constraints are strong, by selection for ecologically relevant phenotypes. We here studied phenotypic disparity in head shape in aquatic snakes. We investigated whether conflicting selective pressures related to different functions have driven shape diversity and explore whether similar phenotypes may give rise to the same functional output (i.e., many‐to‐one mapping of form to function). We focused on the head shape of aquatically foraging snakes as they fulfill several fitness‐relevant functions and show a large amount of morphological variability. We used 3D surface scanning and 3D geometric morphometrics to compare the head shape of 62 species in a phylogenetic context. We first tested whether diet specialization and size are drivers of head shape diversification. Next, we tested for many‐to‐one mapping by comparing the hydrodynamic efficiency of head shape characteristic of the main axes of variation in the dataset. We 3D printed these shapes and measured the forces at play during a frontal strike. Our results show that diet and size explain only a small amount of shape variation. Shapes did not fully functionally converge as more specialized aquatic species evolved a more efficient head shape than others. The shape disparity observed could thus reflect a process of niche specialization.     

The changing times of Europe's largest remaining commercially harvested population of eel Anguilla anguilla L.

This study quantifies the processes involved in regulating the European eel population of Lough Neagh, a lake in Northern Ireland. The relationship between glass eel input and silver eel output for the 1923–1997 cohorts was best described by a Beverton–Holt stock recruitment model. Glass eel input time series was not complete and was thus derived from the relationship between catches elsewhere in Europe and Lough Neagh, together with the addition of stocked glass eel. Silver eel output was the sum of silver eel escapement, catch and yellow eel catch converted to silver eel equivalents. Natural mortality increased with glass eel density, ranging from 0.017 to 0.142 year⁻¹. The mean carrying capacity increased from ≈3.25 M silver eels (≈26 kg ha⁻¹) for the 1923–1943 cohorts to ≈5.0 M (≈40 kg ha⁻¹) for the 1948–1971 cohorts before regressing back to ≈3.25 M. The total silver eel output was highest during the late 1970s/early 1980s at 35–45 kg ha⁻¹ year⁻¹ and lowest during the early years of the 20th century and is currently at 10–15 kg ha⁻¹ year⁻¹. The findings are discussed in relation to (a) the ecological changes that have occurred within the lough, associated with eutrophication and the introduction of roach (Rutilus rutilus L.), and (b) the decline of the wider European eel stock across its distribution range. The findings from this study have relevance for the wider management of the European eel stock.     

赤水河上游主要森林植被中苔藓物种多样性研究

对赤水河上游典型森林植被中苔藓植物多样性调查分析。(1)苔藓植物有15科19属28种(含变种、亚种);生活型有3种：交织型(64.29%)、矮丛集型(28.57%)和平铺型(7.14%)。(2)丰富度以竹叶林中最大(2.131),残存阔叶林中次之(0.687),针叶林中最小(-1.444)。(3)α多样性呈现一定的规律,竹叶林（3.170）＞残存阔叶林（3.000）＞人工植被地（2.807）＞灌木林（2.322）＞针叶林=谷顶区(1.585),α多样性的排序规律与丰富度基本保持一致,均出现在竹叶林中最大。(4)β多样性出现灌木林—残存阔叶林生境中最高（1.000）,竹叶林—残存阔叶林中次之（0.938）,灌木林—针叶林（0.857）中最小的变化差异趋势。分析得出了植被型、湿度和荫蔽度是制约着该地区苔藓植物多样性的主要生态因素。通过苔藓植物多样性的探究,为保护该流域生态环境和生物多样性提供参考价值。     

Structure of Small Mammal Assemblages Across Flooded and Unflooded Gallery Forests of the Amazonia‐Cerrado Ecotone

Habitat heterogeneity may affect the structure of animal assemblages even within apparently homogenous landscapes. Gallery forests of the Amazonia‐Cerrado ecotone have a small‐scale patchiness that is induced by river system dynamics. Gallery forests that never flood are located in upper areas of watercourse margins, whereas seasonally flooded gallery forests are located at lower ground along those margins. We tested the prediction that the assemblage structure of small non‐volant mammals of these two types of forests is distinct and arises from the ecological heterogeneity induced by seasonal floods. We found that species composition differed between forest types, with arboreal species dominating in the seasonally flooded forests and a more balanced distribution of arboreal and terrestrial species in unflooded forests. We found no differences in species abundance between habitats, but species richness was higher in unflooded forests. We hypothesize that this difference is due to decreased resource availability for strictly terrestrial species in seasonally flooded forests. Relative biomass of seasonally flooded forests was more than twice that of unflooded forests due to the dominance of large‐bodied didelphid species in that assemblage. Our results suggest that the ecological heterogeneity created by seasonal floods is central to maintaining diverse assemblages in this region. The preservation of both unflooded and flooded gallery forests, which are under high human pressure from deforestation, agricultural conversion, and implementation of dams, may be crucial to preserving small mammal diversity at the landscape scale.     

Possible influence of increased riparian activity (stream modification and agricultural intensification) on abundance of South African otters

Otters are threatened by habitat loss and the pollution of their riverine habitat. Environmental impacts on top predators are often the first indication of habitat deterioration. It is rare for predator‐prey‐habitats to be monitored over long time intervals (decades), however necessary that may be. Here, we report on the decline in otter relative abundance in a previously pristine habitat and speculate on its causes. We surveyed sign of coexisting otters (Aonyx capensis and Lutra maculicollis) along a river in Kamberg Nature Reserve in uKhahlamba Drakensberg Park, KwaZulu‐Natal, South Africa. The area, Stillerust, lies downstream of a commercial dairy farm and a rural village–subsistence farming area. Data collected recently were compared with two previous surveys, carried out in 1972–1974 and 1993–1994, and were also compared with a pristine section of river in the nature reserve, upstream of the farming areas. At Stillerust, the number of spraint (scat) sites found, for each otter species, approximated only 25% of those recorded in the earlier studies. In the pristine section of the river, the amount of sign and abundance of otters were similar to those recorded in 1993. Assessments of stream biota and water quality analyses revealed negative changes in the river below the pristine area, down to, and including, Stillerust. Visible signs of pollution were evident. Since the 1970s, the rural village population has increased ca eightfold, and the commercial farm has changed from an extensive livestock enterprize to an intensive dairy farm.     

The duplicity of diversity: Caribbean immigrants in Denmark

‘Diversity’ has become a key term in recent years, yet it has been criticized for being a vague concept with different and contradictory meanings. This article demonstrates that there are at least three inherent meanings of the term: (1) discerned difference attributed with positive or negative value; (2) diverting diversity providing pleasure and amusement; and (3) distracting diversity directing attention from something of greater importance. I argue that the concept of diversity can be a fruitful focus in ethnographic research, if its inherent multiplex and duplicitous character is recognized and actively employed. This is shown through an analysis of the ways in which immigrants from the English-speaking Caribbean to Denmark have been perceived and received as foreigners since the 1960s as representing different kinds of diversity.